1 . Field of Invention
This invention relates to the field of road-building and, particularly, to a tamping mechanism of a tie-tamping outfit.
2 . Description of Related Art
Known in the prior art is a tie-tamper (See, e.g., U.S.S.R. publication 629896), comprising a tamping mechanism with a casing mounted on which are tamping tools, hydraulic pumps and hydraulic cylinders articulated to the casing, and a valve unit.
In this known tie-tamping process the tamping tools are moved relative to one another in a longitudinal direction by hydraulic cylinders. The valve unit installed between the hydraulic pumps and hydraulic cylinders transforms the flow of the service fluid into a pulsating flow which ensures the progressive vibratory motion of the tamping tools.
This tamping mechanism is noted for a low effect of vibratory action since it makes no use of hydraulic recoil so that at the end of each hydraulic action part of the service fluid returns through the hydraulic control valve into the tank which calls for utilizing full power of the drive for each following vibrating action. The use of hydraulic cylinders in the capacity of vibrators also impairs the efficiency of the drive due to overflows of the service fluid inside the drive.
Another know tie-tamping machine (See U.S.S.R. publications 1013533) comprises tamping mechanisms mounted on a frame with a provision for being lifted and lowered by a drive, each mechanism comprising a casing with the tamping tools mounted on it and connected with vibrators constituted by hydraulic cylinders. Besides, the tamping mechanism has a hydraulic source of vibration excitation comprising distributing blocks and arresters. The vibrators are rigidly secured on the tamping tool with a provision for horizontal movement while the arresters are installed on the tamping mechanism and linked with an additional hydraulic cylinder.
The tamping mechanism functions as follows. Being acted upon by the vibrator, the tamping tool moves horizontally, the amplitude of this movement being limited by the arresters fixed relative to the casing by the additional hydraulic cylinder. After the tamping tool has penetrated into the ballast, the limiting arresters are displaced by the additional hydraulic cylinder relative to the casing which causes displacement of the central position of the tamping tool while retaining its vibratory displacement from one arrester to the other. This provides for vibratory movement of the tamping tool combined with its displacement in a horizontal plane which ensures compaction of the ballast under the tie.
Thus, the vibratory movement of the tamping tool is ensured by a complicated hydromechanical mechanism comprising a large number of elements of the start-control hydraulic apparatus, and this limits the vibration frequency of the tamping tool and impairs the effect of vibrating action. This requires periodical accelerations and stopping of the tamping tool in extreme positions. The necessity for overcoming the inertia of the tamping tool brings about additional expenditures of power, thus reducing the efficiency of the tamping mechanism. The efficiency of vibrators realized in the form of hydraulic cylinders is limited also by overflows of the service fluid inside the hydraulic cylinders, the extent of the overflows growing in service which curtails the service life of the drive.
Thus, the know mechanism fails to ensure efficient compaction of ballast under the railway ties.